A lot of collisions or slight accidents occur due to invisibility of other vehicles owing to the shape of a road or oncoming vehicles or due to misreading of a position or speed. Accordingly, a DSSS (Driver Safety Support System) receives attention which will be able to reduce accidents by using information obtained by a VICS (Vehicle Information and Communication System) (registered trademark, the mention of which will be omitted from now on) or DSRC (Dedicated Short Range Communication), and demands for implementing road/vehicle coordination service have been increasing. In addition, verification of vehicle-to-vehicle coordination services, which will be able to reduce collisions by communication between vehicles such as an ASV (Advanced Safety Vehicle), has been conducted in advanced countries.
Here, the VICS has three types: a radio beacon system using a 2.5 GHz band radio wave; an infrared beacon system using infrared rays; and an FM multiplex system using an FM radio, and traffic information is delivered from a VICS center using one of them. The DSSS employs an infrared beacon system.
In addition, the DSRC, which is called dedicated short range communication, is a technique that expands a communication technique of an ETC (Electronic Toll Collection System) (registered trademark, the mention of which will be omitted from now on). Its transmission rate reaches 4 Mbps, which is 64 times faster than the transmission rate of 64 kbps of the radio beacon system described above. Recently, using the high rate transmission technique, the next-generation road information providing service is about to be implemented such as IP (Internet Protocol) connection, charge payment at a parking lot, probing for vehicle information and safe-driving support.
As one of the DSSS, a voice guidance device is known which gives several types of information about vehicle traveling such as route information and congestion information in voice (see Patent Document 1, for example). According to the voice guidance device, it sets the degree of priority of voice information used for the voice guidance, and controls in such a manner that when a command is given to output first voice information, it makes a decision as to whether a command to output second voice information with a higher priority than the first voice information is given before the end of the output of the first voice information, and when it decides that the command to output the second voice information is not given before the end of the output of the first voice information, it outputs the first voice information, and when it decides that the command to output the second voice information is given before that, it outputs the second voice information without outputting the first voice information.